Patterns of movement and dispersal in an endangered damselfly and the consequences for its management
James Rouquette, Department of Biological Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK (e-mail J.R.Rouquette@open.ac.uk).
- 1Coenagrion mercuriale is one of Europe's rarest and most threatened damselflies. It is listed in the European Community (EC) Habitats and Species Directive and is the only odonate currently given priority status in the UK Biodiversity Action Plan. Information regarding patterns of movement and dispersal in this species is required to guide conservation and management programmes. Management is currently geared towards habitat restoration of isolated subpopulations, with little attention paid to the metapopulation and landscape context.
- 2A multisite mark–release–recapture project was carried out in the valley of the River Itchen in southern England to determine the extent of movement and the factors affecting movement of mature adults of this endangered damselfly. A total of 8708 individuals was marked.
- 3The species was found to be extremely sedentary, with dispersal limited to an area of contiguous habitat. The median net lifetime movement was 31·9 m and 66% of individuals moved less than 50 m in their lifetime. Movements of greater than 500 m were rare and the longest recorded movement was 1·79 km. This makes it the most sedentary odonate that has been studied in the UK.
- 4The highest recapture rates and the lowest movement distances were recorded at the most isolated site. Time between capture and recapture, and day in season had an effect on movement, and individuals travelled further on their first than on subsequent moves. There was no consistent effect of age or sex on distance moved.
- 5There was strong evidence for inverse density-dependent movement, with individuals moving further in low-density than high-density populations. This is the first time that inverse density-dependent movement has, to our knowledge, been observed in a natural population of odonates.
- 6Synthesis and applications. Coenagrion mercuriale, along with many other invertebrate species of conservation concern, lives in a management-dependent mid-successional habitat. However, the species is highly sedentary. Furthermore, patterns of movement and dispersal are strongly affected by landscape structure and population density. This means that it is unable to recolonize isolated sites and requires ‘stepping stone’ habitats to improve its chances of survival in the medium to long term. Suitable habitat management between sites that are beyond the dispersal distance of individuals can be used to connect or reconnect populations. Within existing sites only small sections of habitat should be managed in any one year and new areas should be created close to existing populations. The long-term persistence of C. mercuriale and other invertebrate species requires a landscape approach to management, with connectivity an important part of management planning. It is clear that carefully conducted studies of movement and dispersal are key components in guiding invertebrate conservation strategies.